L-Tyrosine is linked via a peptide bond to the C-terminus of de-tyrosinated alpha-tubulin (des-Tyromega-alpha-tubulin). The enzyme is highly specific for alpha-tubulin and moderately specific for ATP and L-tyrosine. L-Phenylalanine and 3,4-dihydroxy-L-phenylalanine are transferred but with higher Km values.